These studies are designed to provide quantitative data on the effects of exposure of the prenatal rat to ultrasonic energy. Exposures will be made to graded time intensities of ultrasound at representative times of gestation. Three types of frequency-pulse conditions, which are representative pulse-echo, Doppler, and diathermy techniques will be used. Detailed characterization of the ultrasonic beams will be made, as well as calculations to estimate the energy absorbed by the conceptus. Ongoing measurements of temperature elevations during exposure will be extended and attempts made to detect cavitation. Some of the exposed animals will be sacrificed at 20 days of gestation, prenatal mortality noted, and the fetuses examined in detail for the presence of malformations. To study the genesis of lesions which have been found in previous studies, other rats will be killed serially after exposure. In other experiments the animals will be allowed to deliver and the incidence of mortality and gross anomalies of the offspring determined. The growth and development of the offspring will be studied with particular emphasis on neurological, behavioral, or reproductive deficits or, in some cases, on the cardiovascular system. The incident and absorbed energies associated with various clinical procedures will be estimated. These values will be compared with the "dose-effect" relationships and threshold estimates obtained from these experiments. These will allow an analysis of the safety and/or hazard associated with current clinical techniques.